Permanent waving is intended to set curls in the hair, making use of chemical agents which produce a softening of the cellular structure of the hair and thereafter fix the hair in an altered shape. Prior to the chemical treatment, the hair is usually wound onto very thin (5-16 mm) hair winders. The coiled hair is chemically fixed, so that on completion of the treatment the hair remains deformed in close curls, substantially corresponding to the close windings of the winder.
Such chemical treatment basically represents a heavy stressing of the keratinous cellular structure of the hair and may cause considerable damage to the hair if inexpertly performed. As the name indicates, permanently waved hair permanently maintains its deformation. It is possible to form tight curls (Negroid curls) or gentle soft curls. The decisive factor for the tightness of the curls is the diameter of the winders.
There is also the problem of the aftergrowth of hair which is of course untreated and of a varying degree of straightness. At the latest after approximately six months the difference between the permanently waved and untreated hair is visible and the aftergrowth of hair requires renewed treatment.
As already mentioned, every permanent wave treatment stresses the hair heavily. As far as possible, therefore, the pretreated hair must be protected against being subjected again to chemical stressing which may result in considerable permanent damage, such as splitting, brittleness, dry dullness--in brief, the impression of dead hair. The industry attempts to counteract such damage by the addition of protective substances to the permanent waving agents, since it has hitherto been virtually impossible to effectively separate prewaved and aftergrowth hair, which are of course wound together on a winder, in order to achieve treatment only of the aftergrowth with the chemical agents.